Regulating systems called tourbillons are known where the regulating organ, that is, the sprung balance, is mounted into a carriage rotating about one, two, or three orthogonal pivoting axes permanently driven by a clockwork movement, e.g., a third wheel.
It is the main disadvantage of such systems that rotation of said carriage permanently consumes energy even when this is not necessary, e.g., at night with the watch laid down flat and the sprung balance horizontal.
Moreover, the movements of the carriage may theoretically provide a statistical compensation for the rate variations. While the watch is worn at the wrist, though, it undergoes chance movements, and the rate variations cannot be compensated in full by the constant regular movements imposed upon the sprung balance by the rotating carriage.
From the document EP 1 615 085, a seat correction mechanism for a sprung balance regulating mechanism is known that is held horizontally by counterpoise action. The sprung balance is supported by a platform integral with a counterpoise mounted so as to rotate about a first axis, and pivoted within a carriage mounted so as to rotate about a second axis that is perpendicular to the first one. The escape wheel of the regulating organ meshes with a drive wheel integral with the first axis and forming the output of a first epicycloidal gear train (called “differential” in said document) with three conical planetary wheels, and thus with two conical gears. The inputs of this differential are a corrective first kinematical chain and a driving second kinematical chain, itself attached to the output of a second epicycloidal gear train (called once more “differential” in said document) that has as its input the barrel wheel and a second corrective kinematical chain meshing with a wheel integral with the carriage. In this second differential, three more conical planetary wheels and thus two more conical gears are used, making a total of at least six conical gears for the wheelwork of the mechanism. It should also be noted that all wheels of the first corrective kinematical chain are pivoted on the platform, either concentrically to its axis of rotation or about a fixed axis that is parallel to the latter. In similar fashion, all the wheels of the second corrective kinematical chain are pivoted on the carriage, either concentrically to its axis of rotation or about a fixed axis that is parallel to this axis.
According to document EP 1 615 085, this mechanism effectively allows the regulating organ to be kept in a horizontal plane whatever the position of the watch, solely by the effect of gravity.
However, a major disadvantage of this mechanism consists in the complexity of its wheelwork containing two corrective kinematical chains and a large number of conical gears, particularly so in its epicycloidal gear trains, which causes important power losses and hence necessitates a heavy counterpoise and a large power reserve. Moreover, since all the wheels of these corrective kinematical chains are pivoted on the platform or on the carriage, the weight of this unbalanced system is large, which detracts from the stabilizing effect of the counterpoise.